Jet transport aircraft commonly include a number of flap devices attached to the trailing edges and/or leading edges of each wing of the aircraft. In some aircraft, such as the Boeing 767, the trailing edge flaps are extended and retracted by means of rotary actuators which are mounted to the wing. Each of the rotary actuators includes an actuating arm interconnected with flap linkage that in turn is connected to the flap itself. Rotation of the actuating arm drives the interconnecting flap linkage to extend and retract the flap. The wing has a common drive shaft which is connected to each of the rotary actuators. When an aircrew member moves a flap handle in the cockpit to change the position of the flaps, fluid is directed to a hydraulic motor causing rotation of the common drive shaft and a subsequent change in flap position. The flap motor is designed to develop sufficient torque to drive all of the actuators simultaneously via the common drive shaft. It is generally known however, that hydraulic motors have a very rapid start up rate if the hydraulic flow is not modulated, some accelerating from zero rpm to thousands of rpm in less than a second. This rapid start up rate is opposed by inertial loads, as well as viscous drag loads due to grease in the actuator and linkage bearings, that add to the normal design loads applied to the rotary actuators and flap linkage. In some flap systems these loads are prevented from being transmitted to the actuator by a torque limiter installed in each of the actuators. The torque limiter limits the amount of torque which can be applied from the drive shaft to the actuator. However, the added inertia and viscous drag loads resulting from rapid start up sometimes can result in unwanted actuation of these torque limiters causing lock up of the rotary actuators and preventing further movement of the flaps.
The following patents disclose various apparatus utilized to regulate the flow of a fluidized medium. U.S. Pat. No. 3,001,799--by Plume, discloses an airflow control valve for regulating the flow of air to a vehicle airspring. The airflow control valve includes a spring biased valve member having an axial bypass passageway for directing the flow of air to meet transient airflow demands when the valve member remains seated; the valve member unseating against the bias of the spring during periods of higher airflow demand to uncover a main passageway to meet the higher airflow demand.
A valve for controlling the flow of hydraulic fluid in two directions is disclosed in U.S. Pat. No. 3,093,155--by Dawes, wherein the flow rate is controlled by the position of an axially variable sleeve which is manually positioned at selected axial locations to permit a predetermined flow rate in opposite axial directions, and which may be released from engagement so that the variable sleeve position is controlled by the bias pressure of a spring member.
Hertell, U.S. Pat. No. 3,605,802, discloses a check valve having a spring biased valve member which unseats when incoming hydraulic pressure is sufficient to overcome the spring bias, and wherein movement of the valve member in the open direction is dampened by the displacement of hydraulic fluid.
In U.S. Pat. No. 3,468,341--by Newcomb et al, discloses a valve for precisely controlling vacuum; the valve including a valve member which is moved axially by movement of a diaphram so that a plurality of valve slots are opened to provide progressively increasing cross sectional areas thereby gradually increasing communication of the vacuum through the valve.
Alexander, U.S. Pat. No. 3,621,875, discloses a pressure actuated valve including a poppet member which is biased to a closed position by means of communicating first and a second axially disposed springs in which the first spring is disposed within a hydraulic dashpot to dampen compression of the spring in response to low frequency, longer duration poppet movement, and in which the second spring is undampened and responsive to high frequency, short duration poppet movement.
A control valve for providing a constant volume output in response to varying input pressures is disclosed by Olsson in U.S. Pat. No. 3,809,111, wherein a biased poppet valve is movable axially so that when the poppet is moved in a direction which compresses a spring, flow channels are opened which allow fluid to bypass the poppet valve to a location rearward of the poppet thereby reducing the pressure differential at opposite ends of the poppet to counteract the increased bias resistance of the compressing spring.
In U.S. Pat. No. 3,850,195--by Olsson, there is disclosed a control valve including a valve member repositionable axially within a housing bore by fluid pressure exerted against a spring bias, so that movement of the valve member against the spring bias progressively closes off peripheral passageways utilized for directing the hydraulic fluid around the valve, until all flow of fluid is halted.
In Dubell, U.S. Pat. No. 4,157,012 there is disclosed valve means to prevent pressure perturbations from occurring in a fuel delivery system for a gas turbine engine, wherein the valve means includes a poppet spring biased to a closed position and having an axial passageway in communication with the valve inlet and outlet for conducting small volumes of fluid therethrough when the poppet is closed to maintain a predetermined pressure differential; the valve means including bypass passageways which are opened when the pressure differential across the poppet is sufficient to move the poppet axially against the bias of the spring.
An engine exhaust muffler is disclosed by Dolejsi in U.S. Pat. No. 4,161,996, including a cylindrical member having a valve body which is slidably guided within the cylinder for axial movement so that a number of radially outlet openings are successively covered or uncovered by movement of the valve body to obtain a substantially constant pressure drop across the muffler which is independent of outlet flow.
U.S. Pat. No. 4,350,199--by Bunn et al, discloses a valve assembly including a poppet which is spring biased into a seated closed position, the face of the poppet having grooved portions which receive inlet fluid therein to lower the pressure differential required to open the poppet.